An internal combustion engine is an engine in which a combustion gas generated by combusting fuel directly acts on a piston, a turbine blade, or the like, so that thermal energy of the fuel is converted into mechanical energy. The internal combustion engine may refer to a reciprocation type of engine in which ignition and explosion of a mixed gas of fuel and air occurs in a cylinder to move the piston, and a gas turbine, a jet engine, a rocket engine, and the like are also included as internal combustion engines.
The internal combustion engine may be classified into a gas engine, a gasoline engine, a petroleum engine, a diesel engine, and the like, according to the fuel type for combustion. The petroleum/gas/gasoline engine typically are ignited by an electric spark from a spark plug, and in the diesel engine, the fuel is sprayed at an elevated temperature and an elevated pressure to thereby ignite automatically. In addition, according to the type of stroke and operation of the piston, the internal combustion engine may be a 4-stroke engine or a 2-stroke engine.
The internal combustion engine of a vehicle generally has thermal efficiency of about 15 to 35%, but even at the maximum efficiency of the internal combustion engine, about 60% or greater of the generated thermal energy is emitted to the exterior through a wall of the internal combustion engine, by exhaust gas and the like.
Since reducing an amount of the thermal energy emitted to the exterior through the wall of the internal combustion engine may increase the efficiency of the internal combustion engine, methods such as installing a thermal insulation material at an exterior portion of the internal combustion engine, partially changing a material or a structure of the internal combustion engine, or developing a cooling system of the internal combustion engine have been used.
Particularly, when emission of heat generated by the internal combustion engine to the exterior through the wall of the internal combustion engine is minimized, the efficiency of the internal combustion engine and the fuel efficiency of the vehicle may be improved. However, research into a thermal insulation material, a thermal insulation structure, or the like which is capable of being maintained for an extended period time in the internal combustion engine to which the elevated temperature and the elevated pressure conditions are repeatedly applied has not yet been sufficiently conducted.
In the related arts, methods of using an aerogel for a thermal insulation material, an impact limiter, a soundproofing material, or the like, have been developed. This aerogel may have a structure in which microfilaments having a thickness of about one ten-thousandth the thickness of a human hair are entangled and has porosity of about 90% or greater, and a main material of the aerogel may be a silicon oxide, carbon, or an organic polymer. Particularly, the aerogel material may have a substantially reduced density having improved translucency and significantly reduced thermal conductivity due to the structural features as described above.
However, since the aerogel may not have sufficient strength to thereby be easily broken even by a weak impact due to high brittleness and various thicknesses and shapes may not be produced from the aerogel, use of the aerogel as a thermal insulation material may be limited although the aerogel has improved thermal insulation property. Further, when the aerogel is mixed with other reactants, a solvent or solute may infiltrate into the aerogel and a viscosity of a compound may increase, such that mixing may not be properly performed. Accordingly, when the aerogel composite is formed with other materials or the aerogel is used together with other materials, suitable properties of porous aerogel may not be exhibited.